CONCLUSION DRAWN FROM IN-SITU TESTS ON CONCRETE WITH COMPENSATED SHRINKAGE

Comments are on an in-situ test during which satisfactory characteristics were obtained for concrete with compensated shrinkage. These results were confirmed by those obtained on concrete samples which reached the required values for the different parameters. In order to establish a satisfactory relation between shrinkage compensation, in samples and the real expansion or shrinkage of pavement slabs, numerous measurements of the expansion of the steel reinforcement were taken. These measurements show that during the initial days, concrete expans but that if the latter is let to dry, the resulting shrinkage is not compensated by the previous swelling, the shrinkage being so much more important than the swelling that it leads to cracking of both ordinary and shrinkage-compensated concrete. The first cracks occurred after 130 days in ordinary concrete, but only after 290 days in shrinkage compensated concrete. As regards the chemistry of cement it would be possible to control the formation of ettringite which causes swelling by keeping the aluminates bound to C4A3S. The physical process, originated in Japan which consists in roughly crushing the C4A3S, does not result in the expected increase in time which could enable marked swelling to occur in the concrete, these results lead the author to think that a shrinkage-compensated concrete containing cement, to which C4A3S has been added, is not suitable for normal laying. In order to reduce the maintenance of rigid pavements and to ensure smooth flows, it is suggested that the experience acquired in Austria with shorter slabs be taken into account.